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#221782 07/13/22 10:25 AM
Joined: Mar 2004
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BigB Offline OP
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Curiosity only here, nothing presently in the works. When installing a 50 amp circuit to a 14-50 in the garage for EV or RV use does it get figured into load calculations? I understand that the RV charging stations need to be counted but what about just the 14-50? Also what about a TT-30 for a travel trailer?

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Joined: Jul 2004
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I say they have to be counted and the EV charger is a continuous load. I do understand if it is just a receptacle there might be an argument but I could say the same thing about the dryer receptacle or the range receptacle if the appliances were not there yet.


Greg Fretwell
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Remember the old saying tha figures don’t lie, but liars can figure?

I’d treat the charger for an electric car as a fixed appliance. In most cases, that means using a 75% multiplier.

The RV circuit is another matter. Do we really know how it will be used? Speaking from a design viewpoint — and NOT a code wonk perspective — in most cases I’d treat it as if it were just another small appliance branch circuit (1500 watt adder). If the RV was actually going to be lived in, I’d treat it like a clothes dryer (5000 watts).
If there’s a sewer connection you can assume it will be lived in
I’d be amazed if either circuit were installed with a permit and inspection. Face it: most of the time you’ll learn of these things only after there are problems. At that point you’re likely to find all manner of issues, all the result of decades of remodels and additions.

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BigB Offline OP
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Right now we have an electrical engineer over on the RV forum saying that the listed 50 amp to 30 amp adapters sold for RVs are a code violation. I asked him to post his source.

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The only way you can justify having a 30a circuit protected by a 50a breaker is if you can use the tap rules, using the main breaker in the RV if it is present.


Greg Fretwell
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BigB Offline OP
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My thought is it would be similar to a motor circuit with overload protection at the RV 30 amp main and short circuit at the 50 amp breaker. But then there is the argument, is a TT just a cord and plug connected load or is the TT cord a feeder?

Last edited by BigB; 08/04/22 03:29 PM.
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Code violation? Those are strong words!

Gfretwell is correct. Indeed, there is no requirement that anything plugged into that receptacle be listed or code compliant.. The NEC stops at the breaker. FWIW, the RV plug pattern isn’t found on the NEMA chart.

Apart for use feeding a smaller breaker — and, no, coordination is not required — another possible legitimate use of such an adapter might be in feeding a welder.

Joined: Dec 2002
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Hmm, most RV adapters I have seen adapt a 50 amp 240vac RV cord to a 30 amp 120 vac. I have even seen 50 to 20's for plugging in when at home.

Interesting if a 30 is plugged into a 50 which I have not encountered, but if so, you might be able to squeeze under the tap rules if the RV does have a 30 amp main.

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BigB Offline OP
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I don't think there are many, if any at all, RVs out there without a main breaker.

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G
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Realistically the NEC stops at the face of the permanently installed receptacle. I suspect we are counting on the NRTLs that list the adapters and the industry standards of RV manufacturers to keep them safe.


Greg Fretwell
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